The 'link' between Act and Outlook seems to break itself every day or two, which I can resolve by going in to preferences and re-applying the database location.

Have done a repair install of Office 2013, and therefore Outlook, have created a new Outlook profile from scratch and still continuously get an error message when attempting to view a message from Act:

Re: Act 17 and Outlook 2013 error

After the Office repairs and profile recreation that you've carried out, it would be worthwhile reinstalling Act to ensure that it's correctly identifying Outlook.Could you please report back afterwards if the issue is still occurring?